The present invention relates to a medium- and high-voltage gas-insulated circuit breaker with arc quenching means.
Medium- and high-voltage gas-insulated circuit breakers, such as for example circuit breakers using sulfur hexafluoride (SF.sub.6), air or nitrogen, are conventionally equipped with systems which produce a pressure differential between two separate volumes so as to produce a blast of gas onto the arc region and thus quench the arc.
Thermodynamic systems, which in practice utilize the heat generated by the arc, or mechanical systems, in which a volume of gas is compressed so as to make it flow into the region where the arc is present, are used to generate the pressure differential.
Mechanical generation is normally used whenever the current is unable to generate the intended pressure value thermodynamically.
With mechanical systems for generating the pressure difference, relatively large arcs can be generated in the presence of high currents. Such arcs accordingly obstruct the ducts for exhausting the pressurized gas that should quench the arc, accordingly preventing the discharge of the gas from the gas volume that is compressed. The considerable overpressures that are consequently generated are such as to block the movement of the movable element, thus creating the preconditions for failure to quench the electric arc and jamming of the actuation of the circuit breaker.
Mechanical valves which open when the pressure differentials reach preset levels, so as to reduce the energy required for the actuation system that moves the contacts, have already been used to solve this problem.
However, mechanical valves do not always have a repeatable behavior and are very difficult to calibrate, preventing an assured determination of the pressure differential value that causes the activation thereof.